The present invention relates to a predictive coding/decoding system for block-formed picture signals wherein the block formed picture includes a fraction of pixels (picture elements) due to the block formation.
For a system for coding a picture signal with high efficiency, a predictive coding system is proposed. An example of such a predictive coding system is disclosed in U.S. Pat. No. 4,460,923. The predictive coding system comprises a scan converter in which a plurality of blocks are formed to convert an input video signal into a block formation video signal, a subtractor to make the difference between the block-formation video signal suitably delayed and a prediction signal from a prediction signal generator to be referred to soon to generate a prediction error signal, a quantizer to limit the number of possible levels of the prediction error signal, and a code compressor responsive to the quantized prediction error signal from the quantizer to generate compressed information which will be transmitted to a transmission path. The predictive coding system further comprises an adder for adding the quantized prediction error signal to the prediction signal to generate a locally decoded signal, and the prediction signal generator operative to generate a prediction signal by using the delayed local decoding signal and in accordance with information signifying an optimum prediction function (motion vector) supplied from an optimum prediction or motion detector. Thus, the above-mentioned predictive coding system makes it possible to determine a motion vector in accordance with both motion vector information and prediction error information, thereby providing a remarkably improved coding efficiency especially where the transmission speed is low. Accordingly, such a predictive coding system is especially effective where a television signal undergoes compressive coding and is transmitted at a low speed.
In the above-mentioned predictive coding system, a motion compensated predictive coding system is employed for improving coding efficiency. The motion compensated predictive coding system is to divide a picture signal into a two-dimensional block with m columns and n rows (m and n are positive integers, respectively) to detect the most adaptive block of the previous frame of the previous field by the blocks thus obtained as a unit, thus effecting predictive coding by using the value of pixels within the block as prediction signal. In addition, an entropy coding system for a prediction error signal is to divide a prediction error signal into a two-dimensional block with k columns and 1 rows (k and 1 are positive integers, respectively) to execute an entropy coding processing in the two-dimensional unit, thus providing an improved coding efficiency.
In such a high efficiency coding system for picture signals, signal processing per each two-dimensional block is often employed. However, frequently, there are instances where one picture frame cannot be necessarily divided into m.times.n (or k.times.1) two-dimensional block, namely, the number of pixels of the one picture frame is not equal to a multiple of an integer of m or n (k or 1), resulting in occurrence of a fraction of pixels. However, with the two-dimensional block coding system in such a case, the coding processing in respect to the fraction becomes very complicated. Accordingly, if an attempt is made to completely execute the processing in respect to the fraction, the scale of the system becomes very large.